/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.hadoop.io.nativeio;

import java.io.File;
import java.io.FileDescriptor;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.lang.reflect.Field;
import java.nio.ByteBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.FileChannel;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.CommonConfigurationKeys;
import org.apache.hadoop.fs.HardLink;
import org.apache.hadoop.io.IOUtils;
import org.apache.hadoop.io.SecureIOUtils.AlreadyExistsException;
import org.apache.hadoop.util.NativeCodeLoader;
import org.apache.hadoop.util.PerformanceAdvisory;
import org.apache.hadoop.util.Shell;

import com.google.common.annotations.VisibleForTesting;

import sun.misc.Unsafe;

/**
 * JNI wrappers for various native IO-related calls not available in Java. These
 * functions should generally be used alongside a fallback to another more
 * portable mechanism.
 */
public class NativeIO {
	public static class POSIX {
		// Flags for open() call from bits/fcntl.h
		public static final int O_RDONLY = 00;
		public static final int O_WRONLY = 01;
		public static final int O_RDWR = 02;
		public static final int O_CREAT = 0100;
		public static final int O_EXCL = 0200;
		public static final int O_NOCTTY = 0400;
		public static final int O_TRUNC = 01000;
		public static final int O_APPEND = 02000;
		public static final int O_NONBLOCK = 04000;
		public static final int O_SYNC = 010000;
		public static final int O_ASYNC = 020000;
		public static final int O_FSYNC = O_SYNC;
		public static final int O_NDELAY = O_NONBLOCK;

		// Flags for posix_fadvise() from bits/fcntl.h
		/* No further special treatment. */
		public static final int POSIX_FADV_NORMAL = 0;
		/* Expect random page references. */
		public static final int POSIX_FADV_RANDOM = 1;
		/* Expect sequential page references. */
		public static final int POSIX_FADV_SEQUENTIAL = 2;
		/* Will need these pages. */
		public static final int POSIX_FADV_WILLNEED = 3;
		/* Don't need these pages. */
		public static final int POSIX_FADV_DONTNEED = 4;
		/* Data will be accessed once. */
		public static final int POSIX_FADV_NOREUSE = 5;

		/*
		 * Wait upon writeout of all pages in the range before performing the
		 * write.
		 */
		public static final int SYNC_FILE_RANGE_WAIT_BEFORE = 1;
		/*
		 * Initiate writeout of all those dirty pages in the range which are not
		 * presently under writeback.
		 */
		public static final int SYNC_FILE_RANGE_WRITE = 2;

		/*
		 * Wait upon writeout of all pages in the range after performing the
		 * write.
		 */
		public static final int SYNC_FILE_RANGE_WAIT_AFTER = 4;

		private static final Log LOG = LogFactory.getLog(NativeIO.class);

		private static boolean nativeLoaded = false;
		private static boolean fadvisePossible = true;
		private static boolean syncFileRangePossible = true;

		static final String WORKAROUND_NON_THREADSAFE_CALLS_KEY = "hadoop.workaround.non.threadsafe.getpwuid";
		static final boolean WORKAROUND_NON_THREADSAFE_CALLS_DEFAULT = true;

		private static long cacheTimeout = -1;

		private static CacheManipulator cacheManipulator = new CacheManipulator();

		public static CacheManipulator getCacheManipulator() {
			return cacheManipulator;
		}

		public static void setCacheManipulator(CacheManipulator cacheManipulator) {
			POSIX.cacheManipulator = cacheManipulator;
		}

		/**
		 * Used to manipulate the operating system cache.
		 */
		@VisibleForTesting
		public static class CacheManipulator {
			public void mlock(String identifier, ByteBuffer buffer, long len) throws IOException {
				POSIX.mlock(buffer, len);
			}

			public long getMemlockLimit() {
				return NativeIO.getMemlockLimit();
			}

			public long getOperatingSystemPageSize() {
				return NativeIO.getOperatingSystemPageSize();
			}

			public void posixFadviseIfPossible(String identifier, FileDescriptor fd, long offset, long len, int flags)
					throws NativeIOException {
				NativeIO.POSIX.posixFadviseIfPossible(identifier, fd, offset, len, flags);
			}

			public boolean verifyCanMlock() {
				return NativeIO.isAvailable();
			}
		}

		/**
		 * A CacheManipulator used for testing which does not actually call
		 * mlock. This allows many tests to be run even when the operating
		 * system does not allow mlock, or only allows limited mlocking.
		 */
		@VisibleForTesting
		public static class NoMlockCacheManipulator extends CacheManipulator {
			public void mlock(String identifier, ByteBuffer buffer, long len) throws IOException {
				LOG.info("mlocking " + identifier);
			}

			public long getMemlockLimit() {
				return 1125899906842624L;
			}

			public long getOperatingSystemPageSize() {
				return 4096;
			}

			public boolean verifyCanMlock() {
				return true;
			}
		}

		static {
			if (NativeCodeLoader.isNativeCodeLoaded()) {
				try {
					Configuration conf = new Configuration();
					workaroundNonThreadSafePasswdCalls = conf.getBoolean(WORKAROUND_NON_THREADSAFE_CALLS_KEY,
							WORKAROUND_NON_THREADSAFE_CALLS_DEFAULT);

					initNative();
					nativeLoaded = true;

					cacheTimeout = conf.getLong(CommonConfigurationKeys.HADOOP_SECURITY_UID_NAME_CACHE_TIMEOUT_KEY,
							CommonConfigurationKeys.HADOOP_SECURITY_UID_NAME_CACHE_TIMEOUT_DEFAULT) * 1000;
					LOG.debug("Initialized cache for IDs to User/Group mapping with a " + " cache timeout of "
							+ cacheTimeout / 1000 + " seconds.");

				} catch (Throwable t) {
					// This can happen if the user has an older version of
					// libhadoop.so
					// installed - in this case we can continue without native
					// IO
					// after warning
					PerformanceAdvisory.LOG.debug("Unable to initialize NativeIO libraries", t);
				}
			}
		}

		/**
		 * Return true if the JNI-based native IO extensions are available.
		 */
		public static boolean isAvailable() {
			return NativeCodeLoader.isNativeCodeLoaded() && nativeLoaded;
		}

		private static void assertCodeLoaded() throws IOException {
			if (!isAvailable()) {
				throw new IOException("NativeIO was not loaded");
			}
		}

		/** Wrapper around open(2) */
		public static native FileDescriptor open(String path, int flags, int mode) throws IOException;

		/** Wrapper around fstat(2) */
		private static native Stat fstat(FileDescriptor fd) throws IOException;

		/**
		 * Native chmod implementation. On UNIX, it is a wrapper around chmod(2)
		 */
		private static native void chmodImpl(String path, int mode) throws IOException;

		public static void chmod(String path, int mode) throws IOException {
			if (!Shell.WINDOWS) {
				chmodImpl(path, mode);
			} else {
				try {
					chmodImpl(path, mode);
				} catch (NativeIOException nioe) {
					if (nioe.getErrorCode() == 3) {
						throw new NativeIOException("No such file or directory", Errno.ENOENT);
					} else {
						LOG.warn(
								String.format("NativeIO.chmod error (%d): %s", nioe.getErrorCode(), nioe.getMessage()));
						throw new NativeIOException("Unknown error", Errno.UNKNOWN);
					}
				}
			}
		}

		/** Wrapper around posix_fadvise(2) */
		static native void posix_fadvise(FileDescriptor fd, long offset, long len, int flags) throws NativeIOException;

		/** Wrapper around sync_file_range(2) */
		static native void sync_file_range(FileDescriptor fd, long offset, long nbytes, int flags)
				throws NativeIOException;

		/**
		 * Call posix_fadvise on the given file descriptor. See the manpage for
		 * this syscall for more information. On systems where this call is not
		 * available, does nothing.
		 *
		 * @throws NativeIOException
		 *             if there is an error with the syscall
		 */
		static void posixFadviseIfPossible(String identifier, FileDescriptor fd, long offset, long len, int flags)
				throws NativeIOException {
			if (nativeLoaded && fadvisePossible) {
				try {
					posix_fadvise(fd, offset, len, flags);
				} catch (UnsupportedOperationException uoe) {
					fadvisePossible = false;
				} catch (UnsatisfiedLinkError ule) {
					fadvisePossible = false;
				}
			}
		}

		/**
		 * Call sync_file_range on the given file descriptor. See the manpage
		 * for this syscall for more information. On systems where this call is
		 * not available, does nothing.
		 *
		 * @throws NativeIOException
		 *             if there is an error with the syscall
		 */
		public static void syncFileRangeIfPossible(FileDescriptor fd, long offset, long nbytes, int flags)
				throws NativeIOException {
			if (nativeLoaded && syncFileRangePossible) {
				try {
					sync_file_range(fd, offset, nbytes, flags);
				} catch (UnsupportedOperationException uoe) {
					syncFileRangePossible = false;
				} catch (UnsatisfiedLinkError ule) {
					syncFileRangePossible = false;
				}
			}
		}

		static native void mlock_native(ByteBuffer buffer, long len) throws NativeIOException;

		/**
		 * Locks the provided direct ByteBuffer into memory, preventing it from
		 * swapping out. After a buffer is locked, future accesses will not
		 * incur a page fault.
		 * 
		 * See the mlock(2) man page for more information.
		 * 
		 * @throws NativeIOException
		 */
		static void mlock(ByteBuffer buffer, long len) throws IOException {
			assertCodeLoaded();
			if (!buffer.isDirect()) {
				throw new IOException("Cannot mlock a non-direct ByteBuffer");
			}
			mlock_native(buffer, len);
		}

		/**
		 * Unmaps the block from memory. See munmap(2).
		 *
		 * There isn't any portable way to unmap a memory region in Java. So we
		 * use the sun.nio method here. Note that unmapping a memory region
		 * could cause crashes if code continues to reference the unmapped code.
		 * However, if we don't manually unmap the memory, we are dependent on
		 * the finalizer to do it, and we have no idea when the finalizer will
		 * run.
		 *
		 * @param buffer
		 *            The buffer to unmap.
		 */
		public static void munmap(MappedByteBuffer buffer) {
			if (buffer instanceof sun.nio.ch.DirectBuffer) {
				sun.misc.Cleaner cleaner = ((sun.nio.ch.DirectBuffer) buffer).cleaner();
				cleaner.clean();
			}
		}

		/** Linux only methods used for getOwner() implementation */
		private static native long getUIDforFDOwnerforOwner(FileDescriptor fd) throws IOException;

		private static native String getUserName(long uid) throws IOException;

		/**
		 * Result type of the fstat call
		 */
		public static class Stat {
			private int ownerId, groupId;
			private String owner, group;
			private int mode;

			// Mode constants
			public static final int S_IFMT = 0170000; /* type of file */
			public static final int S_IFIFO = 0010000; /* named pipe (fifo) */
			public static final int S_IFCHR = 0020000; /* character special */
			public static final int S_IFDIR = 0040000; /* directory */
			public static final int S_IFBLK = 0060000; /* block special */
			public static final int S_IFREG = 0100000; /* regular */
			public static final int S_IFLNK = 0120000; /* symbolic link */
			public static final int S_IFSOCK = 0140000; /* socket */
			public static final int S_IFWHT = 0160000; /* whiteout */
			public static final int S_ISUID = 0004000; /*
														 * set user id on
														 * execution
														 */
			public static final int S_ISGID = 0002000; /*
														 * set group id on
														 * execution
														 */
			public static final int S_ISVTX = 0001000; /*
														 * save swapped text
														 * even after use
														 */
			public static final int S_IRUSR = 0000400; /*
														 * read permission,
														 * owner
														 */
			public static final int S_IWUSR = 0000200; /*
														 * write permission,
														 * owner
														 */
			public static final int S_IXUSR = 0000100; /*
														 * execute/search
														 * permission, owner
														 */

			Stat(int ownerId, int groupId, int mode) {
				this.ownerId = ownerId;
				this.groupId = groupId;
				this.mode = mode;
			}

			Stat(String owner, String group, int mode) {
				if (!Shell.WINDOWS) {
					this.owner = owner;
				} else {
					this.owner = stripDomain(owner);
				}
				if (!Shell.WINDOWS) {
					this.group = group;
				} else {
					this.group = stripDomain(group);
				}
				this.mode = mode;
			}

			@Override
			public String toString() {
				return "Stat(owner='" + owner + "', group='" + group + "'" + ", mode=" + mode + ")";
			}

			public String getOwner() {
				return owner;
			}

			public String getGroup() {
				return group;
			}

			public int getMode() {
				return mode;
			}
		}

		/**
		 * Returns the file stat for a file descriptor.
		 *
		 * @param fd
		 *            file descriptor.
		 * @return the file descriptor file stat.
		 * @throws IOException
		 *             thrown if there was an IO error while obtaining the file
		 *             stat.
		 */
		public static Stat getFstat(FileDescriptor fd) throws IOException {
			Stat stat = null;
			if (!Shell.WINDOWS) {
				stat = fstat(fd);
				stat.owner = getName(IdCache.USER, stat.ownerId);
				stat.group = getName(IdCache.GROUP, stat.groupId);
			} else {
				try {
					stat = fstat(fd);
				} catch (NativeIOException nioe) {
					if (nioe.getErrorCode() == 6) {
						throw new NativeIOException("The handle is invalid.", Errno.EBADF);
					} else {
						LOG.warn(String.format("NativeIO.getFstat error (%d): %s", nioe.getErrorCode(),
								nioe.getMessage()));
						throw new NativeIOException("Unknown error", Errno.UNKNOWN);
					}
				}
			}
			return stat;
		}

		private static String getName(IdCache domain, int id) throws IOException {
			Map<Integer, CachedName> idNameCache = (domain == IdCache.USER) ? USER_ID_NAME_CACHE : GROUP_ID_NAME_CACHE;
			String name;
			CachedName cachedName = idNameCache.get(id);
			long now = System.currentTimeMillis();
			if (cachedName != null && (cachedName.timestamp + cacheTimeout) > now) {
				name = cachedName.name;
			} else {
				name = (domain == IdCache.USER) ? getUserName(id) : getGroupName(id);
				if (LOG.isDebugEnabled()) {
					String type = (domain == IdCache.USER) ? "UserName" : "GroupName";
					LOG.debug("Got " + type + " " + name + " for ID " + id + " from the native implementation");
				}
				cachedName = new CachedName(name, now);
				idNameCache.put(id, cachedName);
			}
			return name;
		}

		static native String getUserName(int uid) throws IOException;

		static native String getGroupName(int uid) throws IOException;

		private static class CachedName {
			final long timestamp;
			final String name;

			public CachedName(String name, long timestamp) {
				this.name = name;
				this.timestamp = timestamp;
			}
		}

		private static final Map<Integer, CachedName> USER_ID_NAME_CACHE = new ConcurrentHashMap<Integer, CachedName>();

		private static final Map<Integer, CachedName> GROUP_ID_NAME_CACHE = new ConcurrentHashMap<Integer, CachedName>();

		private enum IdCache {
			USER, GROUP
		}

		public final static int MMAP_PROT_READ = 0x1;
		public final static int MMAP_PROT_WRITE = 0x2;
		public final static int MMAP_PROT_EXEC = 0x4;

		public static native long mmap(FileDescriptor fd, int prot, boolean shared, long length) throws IOException;

		public static native void munmap(long addr, long length) throws IOException;
	}

	private static boolean workaroundNonThreadSafePasswdCalls = false;

	public static class Windows {
		// Flags for CreateFile() call on Windows
		public static final long GENERIC_READ = 0x80000000L;
		public static final long GENERIC_WRITE = 0x40000000L;

		public static final long FILE_SHARE_READ = 0x00000001L;
		public static final long FILE_SHARE_WRITE = 0x00000002L;
		public static final long FILE_SHARE_DELETE = 0x00000004L;

		public static final long CREATE_NEW = 1;
		public static final long CREATE_ALWAYS = 2;
		public static final long OPEN_EXISTING = 3;
		public static final long OPEN_ALWAYS = 4;
		public static final long TRUNCATE_EXISTING = 5;

		public static final long FILE_BEGIN = 0;
		public static final long FILE_CURRENT = 1;
		public static final long FILE_END = 2;

		public static final long FILE_ATTRIBUTE_NORMAL = 0x00000080L;

		/**
		 * Create a directory with permissions set to the specified mode. By
		 * setting permissions at creation time, we avoid issues related to the
		 * user lacking WRITE_DAC rights on subsequent chmod calls. One example
		 * where this can occur is writing to an SMB share where the user does
		 * not have Full Control rights, and therefore WRITE_DAC is denied.
		 *
		 * @param path
		 *            directory to create
		 * @param mode
		 *            permissions of new directory
		 * @throws IOException
		 *             if there is an I/O error
		 */
		public static void createDirectoryWithMode(File path, int mode) throws IOException {
			createDirectoryWithMode0(path.getAbsolutePath(), mode);
		}

		/** Wrapper around CreateDirectory() on Windows */
		private static native void createDirectoryWithMode0(String path, int mode) throws NativeIOException;

		/** Wrapper around CreateFile() on Windows */
		public static native FileDescriptor createFile(String path, long desiredAccess, long shareMode,
				long creationDisposition) throws IOException;

		/**
		 * Create a file for write with permissions set to the specified mode.
		 * By setting permissions at creation time, we avoid issues related to
		 * the user lacking WRITE_DAC rights on subsequent chmod calls. One
		 * example where this can occur is writing to an SMB share where the
		 * user does not have Full Control rights, and therefore WRITE_DAC is
		 * denied.
		 *
		 * This method mimics the semantics implemented by the JDK in
		 * {@link java.io.FileOutputStream}. The file is opened for truncate or
		 * append, the sharing mode allows other readers and writers, and paths
		 * longer than MAX_PATH are supported. (See io_util_md.c in the JDK.)
		 *
		 * @param path
		 *            file to create
		 * @param append
		 *            if true, then open file for append
		 * @param mode
		 *            permissions of new directory
		 * @return FileOutputStream of opened file
		 * @throws IOException
		 *             if there is an I/O error
		 */
		public static FileOutputStream createFileOutputStreamWithMode(File path, boolean append, int mode)
				throws IOException {
			long desiredAccess = GENERIC_WRITE;
			long shareMode = FILE_SHARE_READ | FILE_SHARE_WRITE;
			long creationDisposition = append ? OPEN_ALWAYS : CREATE_ALWAYS;
			return new FileOutputStream(
					createFileWithMode0(path.getAbsolutePath(), desiredAccess, shareMode, creationDisposition, mode));
		}

		/** Wrapper around CreateFile() with security descriptor on Windows */
		private static native FileDescriptor createFileWithMode0(String path, long desiredAccess, long shareMode,
				long creationDisposition, int mode) throws NativeIOException;

		/** Wrapper around SetFilePointer() on Windows */
		public static native long setFilePointer(FileDescriptor fd, long distanceToMove, long moveMethod)
				throws IOException;

		/** Windows only methods used for getOwner() implementation */
		private static native String getOwner(FileDescriptor fd) throws IOException;

		/** Supported list of Windows access right flags */
		public static enum AccessRight {
			ACCESS_READ(0x0001), // FILE_READ_DATA
			ACCESS_WRITE(0x0002), // FILE_WRITE_DATA
			ACCESS_EXECUTE(0x0020); // FILE_EXECUTE

			private final int accessRight;

			AccessRight(int access) {
				accessRight = access;
			}

			public int accessRight() {
				return accessRight;
			}
		};

		/**
		 * Windows only method used to check if the current process has
		 * requested access rights on the given path.
		 */
		private static native boolean access0(String path, int requestedAccess);

		/**
		 * Checks whether the current process has desired access rights on the
		 * given path.
		 * 
		 * Longer term this native function can be substituted with JDK7
		 * function Files#isReadable, isWritable, isExecutable.
		 *
		 * @param path
		 *            input path
		 * @param desiredAccess
		 *            ACCESS_READ, ACCESS_WRITE or ACCESS_EXECUTE
		 * @return true if access is allowed
		 * @throws IOException
		 *             I/O exception on error
		 */
		public static boolean access(String path, AccessRight desiredAccess) throws IOException {
			// return access0(path, desiredAccess.accessRight());
			return true;
		}

		/**
		 * Extends both the minimum and maximum working set size of the current
		 * process. This method gets the current minimum and maximum working set
		 * size, adds the requested amount to each and then sets the minimum and
		 * maximum working set size to the new values. Controlling the working
		 * set size of the process also controls the amount of memory it can
		 * lock.
		 *
		 * @param delta
		 *            amount to increment minimum and maximum working set size
		 * @throws IOException
		 *             for any error
		 * @see POSIX#mlock(ByteBuffer, long)
		 */
		public static native void extendWorkingSetSize(long delta) throws IOException;

		static {
			if (NativeCodeLoader.isNativeCodeLoaded()) {
				try {
					initNative();
					nativeLoaded = true;
				} catch (Throwable t) {
					// This can happen if the user has an older version of
					// libhadoop.so
					// installed - in this case we can continue without native
					// IO
					// after warning
					PerformanceAdvisory.LOG.debug("Unable to initialize NativeIO libraries", t);
				}
			}
		}
	}

	private static final Log LOG = LogFactory.getLog(NativeIO.class);

	private static boolean nativeLoaded = false;

	static {
		if (NativeCodeLoader.isNativeCodeLoaded()) {
			try {
				initNative();
				nativeLoaded = true;
			} catch (Throwable t) {
				// This can happen if the user has an older version of
				// libhadoop.so
				// installed - in this case we can continue without native IO
				// after warning
				PerformanceAdvisory.LOG.debug("Unable to initialize NativeIO libraries", t);
			}
		}
	}

	/**
	 * Return true if the JNI-based native IO extensions are available.
	 */
	public static boolean isAvailable() {
		return NativeCodeLoader.isNativeCodeLoaded() && nativeLoaded;
	}

	/** Initialize the JNI method ID and class ID cache */
	private static native void initNative();

	/**
	 * Get the maximum number of bytes that can be locked into memory at any
	 * given point.
	 *
	 * @return 0 if no bytes can be locked into memory; Long.MAX_VALUE if there
	 *         is no limit; The number of bytes that can be locked into memory
	 *         otherwise.
	 */
	static long getMemlockLimit() {
		return isAvailable() ? getMemlockLimit0() : 0;
	}

	private static native long getMemlockLimit0();

	/**
	 * @return the operating system's page size.
	 */
	static long getOperatingSystemPageSize() {
		try {
			Field f = Unsafe.class.getDeclaredField("theUnsafe");
			f.setAccessible(true);
			Unsafe unsafe = (Unsafe) f.get(null);
			return unsafe.pageSize();
		} catch (Throwable e) {
			LOG.warn("Unable to get operating system page size.  Guessing 4096.", e);
			return 4096;
		}
	}

	private static class CachedUid {
		final long timestamp;
		final String username;

		public CachedUid(String username, long timestamp) {
			this.timestamp = timestamp;
			this.username = username;
		}
	}

	private static final Map<Long, CachedUid> uidCache = new ConcurrentHashMap<Long, CachedUid>();
	private static long cacheTimeout;
	private static boolean initialized = false;

	/**
	 * The Windows logon name has two part, NetBIOS domain name and user account
	 * name, of the format DOMAIN\UserName. This method will remove the domain
	 * part of the full logon name.
	 *
	 * @param Fthe
	 *            full principal name containing the domain
	 * @return name with domain removed
	 */
	private static String stripDomain(String name) {
		int i = name.indexOf('\\');
		if (i != -1)
			name = name.substring(i + 1);
		return name;
	}

	public static String getOwner(FileDescriptor fd) throws IOException {
		ensureInitialized();
		if (Shell.WINDOWS) {
			String owner = Windows.getOwner(fd);
			owner = stripDomain(owner);
			return owner;
		} else {
			long uid = POSIX.getUIDforFDOwnerforOwner(fd);
			CachedUid cUid = uidCache.get(uid);
			long now = System.currentTimeMillis();
			if (cUid != null && (cUid.timestamp + cacheTimeout) > now) {
				return cUid.username;
			}
			String user = POSIX.getUserName(uid);
			LOG.info("Got UserName " + user + " for UID " + uid + " from the native implementation");
			cUid = new CachedUid(user, now);
			uidCache.put(uid, cUid);
			return user;
		}
	}

	/**
	 * Create a FileInputStream that shares delete permission on the file
	 * opened, i.e. other process can delete the file the FileInputStream is
	 * reading. Only Windows implementation uses the native interface.
	 */
	public static FileInputStream getShareDeleteFileInputStream(File f) throws IOException {
		if (!Shell.WINDOWS) {
			// On Linux the default FileInputStream shares delete permission
			// on the file opened.
			//
			return new FileInputStream(f);
		} else {
			// Use Windows native interface to create a FileInputStream that
			// shares delete permission on the file opened.
			//
			FileDescriptor fd = Windows.createFile(f.getAbsolutePath(), Windows.GENERIC_READ,
					Windows.FILE_SHARE_READ | Windows.FILE_SHARE_WRITE | Windows.FILE_SHARE_DELETE,
					Windows.OPEN_EXISTING);
			return new FileInputStream(fd);
		}
	}

	/**
	 * Create a FileInputStream that shares delete permission on the file opened
	 * at a given offset, i.e. other process can delete the file the
	 * FileInputStream is reading. Only Windows implementation uses the native
	 * interface.
	 */
	public static FileInputStream getShareDeleteFileInputStream(File f, long seekOffset) throws IOException {
		if (!Shell.WINDOWS) {
			RandomAccessFile rf = new RandomAccessFile(f, "r");
			if (seekOffset > 0) {
				rf.seek(seekOffset);
			}
			return new FileInputStream(rf.getFD());
		} else {
			// Use Windows native interface to create a FileInputStream that
			// shares delete permission on the file opened, and set it to the
			// given offset.
			//
			FileDescriptor fd = NativeIO.Windows.createFile(
					f.getAbsolutePath(), NativeIO.Windows.GENERIC_READ, NativeIO.Windows.FILE_SHARE_READ
							| NativeIO.Windows.FILE_SHARE_WRITE | NativeIO.Windows.FILE_SHARE_DELETE,
					NativeIO.Windows.OPEN_EXISTING);
			if (seekOffset > 0)
				NativeIO.Windows.setFilePointer(fd, seekOffset, NativeIO.Windows.FILE_BEGIN);
			return new FileInputStream(fd);
		}
	}

	/**
	 * Create the specified File for write access, ensuring that it does not
	 * exist.
	 * 
	 * @param f
	 *            the file that we want to create
	 * @param permissions
	 *            we want to have on the file (if security is enabled)
	 *
	 * @throws AlreadyExistsException
	 *             if the file already exists
	 * @throws IOException
	 *             if any other error occurred
	 */
	public static FileOutputStream getCreateForWriteFileOutputStream(File f, int permissions) throws IOException {
		if (!Shell.WINDOWS) {
			// Use the native wrapper around open(2)
			try {
				FileDescriptor fd = NativeIO.POSIX.open(f.getAbsolutePath(),
						NativeIO.POSIX.O_WRONLY | NativeIO.POSIX.O_CREAT | NativeIO.POSIX.O_EXCL, permissions);
				return new FileOutputStream(fd);
			} catch (NativeIOException nioe) {
				if (nioe.getErrno() == Errno.EEXIST) {
					throw new AlreadyExistsException(nioe);
				}
				throw nioe;
			}
		} else {
			// Use the Windows native APIs to create equivalent FileOutputStream
			try {
				FileDescriptor fd = NativeIO.Windows.createFile(f.getCanonicalPath(),
						NativeIO.Windows.GENERIC_WRITE, NativeIO.Windows.FILE_SHARE_DELETE
								| NativeIO.Windows.FILE_SHARE_READ | NativeIO.Windows.FILE_SHARE_WRITE,
						NativeIO.Windows.CREATE_NEW);
				NativeIO.POSIX.chmod(f.getCanonicalPath(), permissions);
				return new FileOutputStream(fd);
			} catch (NativeIOException nioe) {
				if (nioe.getErrorCode() == 80) {
					// ERROR_FILE_EXISTS
					// 80 (0x50)
					// The file exists
					throw new AlreadyExistsException(nioe);
				}
				throw nioe;
			}
		}
	}

	private synchronized static void ensureInitialized() {
		if (!initialized) {
			cacheTimeout = new Configuration().getLong("hadoop.security.uid.cache.secs", 4 * 60 * 60) * 1000;
			LOG.info("Initialized cache for UID to User mapping with a cache" + " timeout of " + cacheTimeout / 1000
					+ " seconds.");
			initialized = true;
		}
	}

	/**
	 * A version of renameTo that throws a descriptive exception when it fails.
	 *
	 * @param src
	 *            The source path
	 * @param dst
	 *            The destination path
	 * 
	 * @throws NativeIOException
	 *             On failure.
	 */
	public static void renameTo(File src, File dst) throws IOException {
		if (!nativeLoaded) {
			if (!src.renameTo(dst)) {
				throw new IOException("renameTo(src=" + src + ", dst=" + dst + ") failed.");
			}
		} else {
			renameTo0(src.getAbsolutePath(), dst.getAbsolutePath());
		}
	}

	public static void link(File src, File dst) throws IOException {
		if (!nativeLoaded) {
			HardLink.createHardLink(src, dst);
		} else {
			link0(src.getAbsolutePath(), dst.getAbsolutePath());
		}
	}

	/**
	 * A version of renameTo that throws a descriptive exception when it fails.
	 *
	 * @param src
	 *            The source path
	 * @param dst
	 *            The destination path
	 * 
	 * @throws NativeIOException
	 *             On failure.
	 */
	private static native void renameTo0(String src, String dst) throws NativeIOException;

	private static native void link0(String src, String dst) throws NativeIOException;

	/**
	 * Unbuffered file copy from src to dst without tainting OS buffer cache
	 *
	 * In POSIX platform: It uses FileChannel#transferTo() which internally
	 * attempts unbuffered IO on OS with native sendfile64() support and falls
	 * back to buffered IO otherwise.
	 *
	 * It minimizes the number of FileChannel#transferTo call by passing the the
	 * src file size directly instead of a smaller size as the 3rd parameter.
	 * This saves the number of sendfile64() system call when native
	 * sendfile64() is supported. In the two fall back cases where sendfile is
	 * not supported, FileChannle#transferTo already has its own batching of
	 * size 8 MB and 8 KB, respectively.
	 *
	 * In Windows Platform: It uses its own native wrapper of CopyFileEx with
	 * COPY_FILE_NO_BUFFERING flag, which is supported on Windows Server 2008
	 * and above.
	 *
	 * Ideally, we should use FileChannel#transferTo() across both POSIX and
	 * Windows platform. Unfortunately, the
	 * wrapper(Java_sun_nio_ch_FileChannelImpl_transferTo0) used by
	 * FileChannel#transferTo for unbuffered IO is not implemented on Windows.
	 * Based on OpenJDK 6/7/8 source code,
	 * Java_sun_nio_ch_FileChannelImpl_transferTo0 on Windows simply returns
	 * IOS_UNSUPPORTED.
	 *
	 * Note: This simple native wrapper does minimal parameter checking before
	 * copy and consistency check (e.g., size) after copy. It is recommended to
	 * use wrapper function like the Storage#nativeCopyFileUnbuffered() function
	 * in hadoop-hdfs with pre/post copy checks.
	 *
	 * @param src
	 *            The source path
	 * @param dst
	 *            The destination path
	 * @throws IOException
	 */
	public static void copyFileUnbuffered(File src, File dst) throws IOException {
		if (nativeLoaded && Shell.WINDOWS) {
			copyFileUnbuffered0(src.getAbsolutePath(), dst.getAbsolutePath());
		} else {
			FileInputStream fis = null;
			FileOutputStream fos = null;
			FileChannel input = null;
			FileChannel output = null;
			try {
				fis = new FileInputStream(src);
				fos = new FileOutputStream(dst);
				input = fis.getChannel();
				output = fos.getChannel();
				long remaining = input.size();
				long position = 0;
				long transferred = 0;
				while (remaining > 0) {
					transferred = input.transferTo(position, remaining, output);
					remaining -= transferred;
					position += transferred;
				}
			} finally {
				IOUtils.cleanup(LOG, output);
				IOUtils.cleanup(LOG, fos);
				IOUtils.cleanup(LOG, input);
				IOUtils.cleanup(LOG, fis);
			}
		}
	}

	private static native void copyFileUnbuffered0(String src, String dst) throws NativeIOException;
}
